The Italian and English champions played out a goalless draw at the San Siro, but Mourinho does not think that United will gain a major advantage from playing at home in the second-leg.
"I think that the result is difficult for us, because we can't lose at Old Trafford, but also for them, because with a score draw we will qualify," the former Chelsea boss said.
"It's a result that will put pressure on both sides."
AcceptThe home side made a sluggish start and Sir Alex Ferguson's team dominated the first-half. However, Inter regrouped during half-time and began to create chances after the break.
Mourinho thinks that the result fairly reflected the efforts of either side.
"In the first-half Manchester United did better than us, in the second one we did better than them. Because of this, the result must be accepted."
The Portuguese manager praised the efforts of striker Zlatan Ibrahimovic despite the Swede not being very lively in front of goal. He also hailed 18-year-old defender Davide Santon, who made his first appearance in Europe's top club competition.
"It seems to me that Ibra had a good match. Manchester aren't Bologna," Mourinho added.
"In a match like this I think it's right to also talk about Santon, who made his debut in the Champions League and I think he put in a positive performance."